1. Field
The embodiments discussed herein are directed to a substrate processing apparatus and a substrate processing method.
2. Description of the Related Art
In a manufacturing process of a semiconductor device such as a large-scale integrated circuit (LSI), a semiconductor substrate undergoes a cleaning process in order to remove a native oxide film formed on a surface of the semiconductor substrate, or to remove photoresist residues. A substrate processing apparatus used in the cleaning process is roughly categorized into a batch-type apparatus and a sheet-type apparatus. From a viewpoint of obtaining higher throughput, the batch-type apparatus capable of cleaning multiple semiconductor substrates in one cleaning session is more advantageous than the sheet-type apparatus configured to process the semiconductor substrates individually.
Nevertheless, since the multiple semiconductor substrates are dipped in a single liquid tank in the case of the batch-type apparatus, there is a problem that particles formerly attached to a rear surface of a certain semiconductor substrate get attached to a front surface (a circuit formation surface) of another semiconductor. Such a problem is called backside transfer of particles, which is responsible for a reduction in the yield of semiconductor devices. Particularly, along with miniaturization of semiconductor devices in recent years, the allowable size of particles is becoming smaller every year. Today, the allowable value of particles, which may float in a liquid tank, is equal to or below 0.1 μm.
To prevent such backside transfer of particles as much as possible, the batch-type substrate processing apparatus includes a foreign substance removal mechanism called a CRS (chemical recovery system). The CRS is integrally formed by a filter for filtering particles and a circulation pump. This mechanism can circulate a liquid in the liquid tank and, at the same time, can filter the particles in the liquid. Thus, it is possible to reduce the number of particles that are peeled off from the rear surfaces of the semiconductor substrates and are floating in the liquid.
However, even though the CRS is provided therein, a long period of time is required for reducing the number of particles in the liquid tank to an allowable level, if a lot of particles are brought into the liquid tank at a time. In this case, the throughput of the substrate processing apparatus is considerably decreased.
To deal with this case, for each of the liquid tanks, limits are currently set as to how many times the processing can be performed, or how much time it can take. In a case where the processing exceeds the limits, the liquid is replaced so as to prevent the decrease in the throughput. However, when the liquid is frequently replaced in this manner, there arises another problem of an increase in usage of the liquid, which leads to an increase in the cleaning cost in the batch-type substrate processing apparatus.
Meanwhile, there is also a case where a spin-scrubber process is performed prior to processing the substrate with the substrate processing apparatus, so that the number of particles which are brought into the liquid tank is reduced. However, this process causes another problem of an increase in the manufacturing cost of the semiconductor device which is relevant to the spin-scrubber process.
Some techniques related to the present invention are disclosed in Japanese Unexamined Patent Application Publication No. 56 (1981)-60021, Japanese Patent Application Laid-open Publication No. Hei 8 (1996)-197418 and Japanese Patent Application Laid-open Publication No. 2005-175053.